/Engine/Source/Runtime/Core/Public/Misc/FileHelper.h
Generates the next unique bitmap filename with a specified extension
true if success
static void GenerateDateTimeBasedBitmapFilename ( const [FString](API\Runtime\Core\Containers\FString) & Pattern, const [FString](API\Runtime\Core\Containers\FString) & Extension, [FString](API\Runtime\Core\Containers\FString) & OutFilename )